Center image on the plate

Hello guys,
i would know the mode to center the image on the plate on my Agfa Avalon N8,
the technicals said me the mode, but i had forget it.
I must enter in the service mode, insert the password 8600 and then? What menu i must select? For more of you this is a very easy operation, but i had do it later time ago, but excuse me i don't remember.
Thank's for all reply.